1. Field of the Invention
This invention relates to an apparatus for analyzing physical properties and/or composition of a small area of a specimen, for finely working a specimen or for reforming a surface of a specimen using a high energy charge beam such as an ion beam in various industrial fields including the technical field of semiconductors, the medical and biological technical fields and so forth, and also to various components of such an apparatus including a device for analyzing a crystal structure of a specimen, a quadruple pole magnetic lens, an objective slit device and a specimen chamber.
2. Description of the Prior Art
In the technical field of semiconductors, increase of the storage capacity and increase of the information processing speed are demanded in order to process a large amount of information on a computer. To this end, development of high integration of ICs has been directed from LSIs to VLSIs and further to three dimensional ICs. As such development proceeds, individual elements and wires for those elements are remarkably reduced in size and increased in layers and besides use of a very shallow region under a surface is proceeding. In such investigation of ICs and processes, an ion beam converged to a microscopic size makes a very effective means. For example, in production, maskless implantation is made possible and the production process can be simplified significantly using a converged ion beam accelerated to several hundreds eV to several MeV. On the other hand, in analysis, an analysis of an atom distribution in a microscopic area is very important, and to this end, the effectiveness of an analyzing technique such as the Rutherford backscattering method (RBS) or the particle exciting X-ray spectroscopic method (PIXE) which uses a converged ion beam of a high energy (MeV) and has a resolution smaller than 1 .mu.m is recognized. Thus, improvement in function of such apparatus is being proceeded.
FIG. 16 illustrates an exemplary one of a high energy converged ion beam apparatus which is used as an analyzing apparatus. Referring to FIG. 16, a high energy ion beam 104 generated from an ion source 102 of an accelerator 101 and accelerated by an accelerator tube 103 is first deflected, while passing through a deflecting analyzing electromagnet 106 having a coil 107, by an angle normally greater than 15 degrees so that it is classified in ion type and energy. Subsequently, the high energy ion beam 104 is restricted to several tens .mu.m by an objective collimator or slit member 105 and then, after passing a drift space of 2 to 5 m, introduced into and converged by two or three series of quadruple pole magnetic lenses 112 so that it forms a beam spot on a target 114 accommodated in a specimen chamber 113, that is, on a specimen to be measured. A detector 115 detects ions or an excited X-ray radiated from the target 114.
The distance of a drift space from the objective collimator 105 to the quadruple pole magnetic lenses 112 is called an object distance while the distance from the lenses 112 to the target 114 is called an image distance, and the present optical system has a function of converging an aperture of the objective collimator 105 at a rate of reduction substantially equal to a rate between the two distances and irradiating the thus converged aperture upon the target 114. By the way, since the image distance is 100 to 200 mm or so because an accommodation spacing for the detector 115 and so forth is required, in order to make a beam spot further smaller and/or to further raise the current density to achieve improvement of performances of the system, the object distance must be further increased.
In the conventional converged ion beam apparatus described above, a route of a beam including the distance from the accelerator 101 to the deflecting analyzing electromagnet 106 and the distance from the electromagnet 106 to the specimen chamber 113 requires at least 7 m or more. Besides, since the deflecting angle of an ion beam is greater than 15 degrees in order to classify a type of ions by means of the deflecting analyzing electromagnet 106, an ion beam is expanded also in a lateral direction, an in an actual arrangement, a spacing greater than about 7 m .times.3 m is required, which makes, rather than an apparatus, an equipment having such a horizontal extent that may fully occupy a room.
Besides, reverse disadvantages are caused by an increase in size of an apparatus, and in particular, in order to converge an ion beam to a spot size of about 1 .mu.m, it is necessary to perform initial adjustment strictly and, further as a maintaining operation, precisely maintain alignment of the optical system wherein centers and axial lines of individual components are made coinncide with each other. In this instance, an alignment adjusting operation between components disposed along a beam line which is deflected by an angle greater than 15 degrees is further difficult. Further, since the apparatus is great in size, integration of a platform for the prevention of vibrations is almost impossible.
Meanwhile, in order to converge an ion beam of a high energy (MeV) with such a conventional converged ion beam apparatus, a strong lens system is required which is higher by 1,000 times in resolution compared with an ordinary electron microscope. To this end, utilization is considered of a nonaxisymmetic lens such as a quadruple pole lens (for example, Nuclear Instrument and Methods 197 (1982), pp. 65-77).
FIG. 17 shows a magnetic pole body of an exemplary one of conventional quadruple pole lenses. Referring to FIG. 17, the magnetic pole body includes a cylindrical return yoke 124 and four magnetic poles 123 secured to the cylindrical return yoke 124 by means of fastening bolts 125. The magnetic pole body is shown in a disassembled condition in FIG. 18.
Generally, the converging force k of an ion beam by a quadruple pole lens is represented as ##EQU1## where e is charge of ions, E beam energy, M a mass of ions, N a number of coils of a winding, I a coil current, and r.sub.B a bore diameter. The converging force k thus increases in inverse proportion to the bore diameter r.sub.B, that is, to a radius of an inscribed circle to such four magnetic poles shown in FIG. 17. Accordingly, a very strong converging force is obtained as the bore radius is decreased.
Recently, the necessity has arisen for a quadruple pole magnetic lens having a high degree of accuracy and a strong converging force and having a bore radius smaller than 3 mm for the object of formation or the like of a microscopic ion beam of high energy, but a bore radius greater than 10 mm is a common limit with such conventional structure as shown in FIG. 17.
The following problems reside in obtaining a very small bore radius comparing with a radius of a return yoke in order to obtain a very strong converging force of an ion beam with regard to a quadruple pole lens. In particular, with the conventional structure of FIG. 17, if it is attempted to only make the bore radius smaller than 3 mm while the return yoke radius is left to be, for example, greater than 150 mm from the necessity to provide a sufficient magnetomotive force, that is, a sufficient coil sectional area, then each magnetic pole will have a radially elongated configuration. Consequently, the accuracy in position of the magnetic poles will rely delicately upon an accuracy in assembly thereof to the return yoke, and accordingly, it is difficult from the accuracy in structure to assure a predetermined relational accuracy or tolerance of the magnetic poles (smaller than .+-.1 .mu.m in a radial direction, and smaller than 0.01 degree in relative angle).
Accordingly, with the conventional structure, the accuracy in arrangement of the magnetic poles is so low that the magnetic field distribution is displaced from a hyperbolic distribution and the aberration is increased, and it is difficult to form a fine spot of a beam. For example, in an optical system wherein a microscopic beam of 1 .mu.m is obtained using a lens having a bore radius, for example, of 2.5 mm, displacement of an end of a magnetic pole only by several .mu.m will cause blurring of a beam spot by an amount greater than several .mu.m.
By the way, in order to obtain a diameter of 1 .mu.m as a minimum beam spot with such a conventional converged ion beam apparatus described hereinabove with reference to FIG. 16, since the reduction rate normally ranges substantially from 1/5 to 1/30, it is necessary to converge a beam to the diameter of 5 to 30 .mu.m by means of the objective slit member or collimator 105, and 1 .mu.m is required for the tolerance in movement of an edge of the slit member.
As a conventional slit device, it is convenient to use a plate in which a small hole through which a beam is to pass is perforated. However, it is impossible to change the diameter of a beam with the slit plate. In applications for a local analysis or fine working of a small area, generally it is sometimes necessary to arbitrarily change the size of a beam spot. Accordingly, a mechanism is employed wherein wedge-shaped knife edge members or cylindrical edge members of metal are opposed from four directions to each other such that the shape of a beam passing therethrough is controlled by a change of the shape of the slit defined by those edge members. In a certain conventional slit device, a wedge-shaped edge member is mounted at an end of each of precision driving mechanism sections such as micrometer heads, and an opening width of a slit defined by the edge members is estimated from graduations of the micrometer heads of the individual edges.
FIG. 19a illustrates, in front elevation, an exemplary one of conventional slit devices having electrically driven adjusting mechanism sections employing piezoelectric elements in place of micrometer heads. Either a pair of knife-shaped edge members 131 or such a pair of wedge-shaped edge members 131' as shown in a vertical sectional side elevational view of FIG. 19b are mounted in an opposing relationship at free ends of arms 133 individually supported on a vacuum duct wall 134 by means of flexible joints 148, and voltages to be applied to piezoelectric elements 149 located behind the edge members 131 are adjusted so as to set a width of a slit between the wedge-shaped edge members 131 through which an ion beam is to pass along a beam line BL as indicated by an arrow mark in FIG. 19b.
In the conventional slit device described above, when it is intended to completely close the slit to find out a zero position at which the opening width of the slit is equal to zero, since there is a local gap between edges of the slit even in a condition wherein the edges contact with each other due to an imperfection in flatness of surfaces of the wedge-shaped or cylindrical edge members (it is inevitable from the point of accuracy in working that an unevenness or an inclination of .mu.m or so exists), an ion beam will leak by way of the local gap, and consequently, the zero point cannot be determined precisely. If the zero point cannot be determined, then it is impossible to set the slit opening width on the order of .mu.m with a high degree of accuracy. Meanwhile, if an operation is performed to compulsorily contact the edges with each other so as to assure a perfectly closed condition, then an excessive load is applied to ends of the edges or to the high precision driving mechanism sections, which makes a cause of deformation at an end of an edge or play of the driving mechanism sections. After all, the conventional slit device cannot achieve satisfactory determination of a zero point in practical use. Accordingly, the setting and control of an opening width of a slit with a required degree of accuracy is impossible.
Further, the amount of heat generated by that part of an ion beam which collides with ends of the edges of the slit is estimated to be several W or more. Since the edge members are placed in a vacuum, such heat is all transmitted to arms or posts on which the edge members are supported. In the conventional slit device, since wedge-shaped or cylindrical edge members are supported on arms and/or posts, the variation of the opening width of the slit which is caused by thermal expansion at the elements presents an unignorable amount. In fact, in the conventional slit device, a current variation of an ion beam arising from such variation on the order of several to several tens .mu.m is observed during use of the device.
In addition, in the conventional slit device, since such a mechanism is employed that two opposing edge members are operated independently of each other to set the opening width of the slit, two times of operation for the opposite sides are required in order to set an arbitrary slit opening width while keeping the center of the slit fixed. Also when it is intended to set the center position of the slit while keeping the opening width of the slit fixed in order to adjust axes of a beam and an optical system, two times of operation for the opposite sides are required. Accordingly, the operability is low in a similar manner.
On the other hand, a conventional channeling measuring beam line which may be employed in such a conventional converged ion beam apparatus as described hereinabove with reference to FIG. 16 normally has such an arrangement as shown in FIG. 20. Referring to FIG. 20, a beam 152 of charged particles such as protons or helium ions generated from an accelerator (not shown) of several MeV of the Van de Graaff type is collimated to a spread angle of 0.01 degrees or so by two upstream and downstream slit devices 153 and 150 and irradiated upon a specimen 156 such as a specimen of single crystal on a biaxial goniometer 155. Ions backscattered from the specimen 156 are normally detected by a semiconductor detector 157 of the silicon surface barrier type and then amplified by an amplifier 158 outside the tank 151, whereafter they are analyzed in energy by a multichannel pulse-height analyzer 159.
The performance of the channeling measurement by the two slit devices 153 and 150 can be geometrically led out from a diagrammatic view of FIG. 21. First, parameters are defined in the following manner.
.alpha.: maximum spread angle (divergence angle) of a beam irradiated upon a surface of a specimen 156 PA0 .beta.: maximum spread angle (divergence angle) of an incident beam PA0 d.sub.1 : opening of the upstream slit device 153 PA0 d.sub.2 : opening of the downstream slit device 150 PA0 L': distance between the upstream and downstream slit devices 153 and 150
When the downstream slit device 150 satisfies a condition 2L'.beta.&gt;d.sub.2 in which it operates effectively, the spread angle .alpha. defined by the two slit devices 153 and 150 is equal to an angle which is provided by two alternate long and short dash lines in FIG. 21 which interconnect opposing edges of the upstream and downstream slit devices 153 and 150 and is given by the following expression. ##EQU2##
Since the apertures of the upstream and downstream slit devices appear in the form of a sum as a numerator in the expression above, it can be recognized that it is necessary to reduce the opening widths of the two slits equally to each other in order to raise the parallelism of a beam. By placing d.sub.1 =d.sub.2 .about.d, ##EQU3##
Meanwhile, a ratio .eta. of those of ions passing through the upstream slit device 153 which pass through the downstream slit device 150 is, if it is evaluated approximately that ions are distributed uniformly in a divergent cone, given by ##EQU4##
In particular, it can be seen that, while the spread angle .alpha. decreases in proportion as d decreases, the ion current decreases in proportion to a square of d.
Particularly, if ordinary parameter values .beta.=1 mrad (0.06 degrees), d.sub.1 =d.sub.2 1 mm and L'=3 m are substituted into the expressions above, then .alpha.=0.7 mrad (0.04 degrees) and .eta.=0.063 (6.3%) are obtained.
Manners of cutting of a beam by the upstream and downstream slit devices 153 and 150 in a phase space are represented as shown in lower phase views A' to D' of FIG. 21.
If it is assumed that an incident beam has a circular emittance in a phase space, it is cut to a vertically elongated shape by the upstream slit device 153 (view A'). Then, while the incident beam advances in a drift space of the length L', it is deformed in accordance with conversions of x.fwdarw.x+x'L' and x'.fwdarw.x' (view B'), and then it is cut by the downstream slit device 150 so that it may have a further reduced spread angle .alpha. (view C'). Thus, the beam presents such a shape as seen in the view D' at a surface of a specimen 156. Accordingly, it can be recognized that also in a phase space, as the drift space increases, the spread angle of a beam cut by the downstream slit device decreases.
Such a conventional double slit system has the following fundmental problems as can be recognized from the analysis described above.
While it is necessary either to reduce both of the apertures of the two slit devices or to increase the distance between the two slit devices in order to raise the parallelism of an ion beam to be irradiated, an irradiation ion current is sacrificed in either case. In particular, since the cutting efficiency of an incident ion beam is low, it can be utilized only at a low rate as an irradiation ion current. Accordingly, if a practical measurement is made possible, then it cannot be anticipated to improve the performance further than actual results at present.
Anyway, the conventional double slit system requires assurance of a long beam line by all means, which makes construction of an apparatus difficult in various respects.
Where such a conventional converged ion beam apparatus as described hereinabove with reference to FIG. 16 is used as an ion beam analyzing apparatus, ions, electrons, photons and so forth which are radiated from a surface of a specimen 114 by irradiation of an ion beam 104 upon the specimen 114 are detected by the detector 115 in the specimen chamber 113 to analyze a type, energy, and angle and so forth of the radiated particles in order to obtain atom distribution information at a position very near to the surface of the specimen 114 or in a zone from the surface to the inside of the specimen 114.
Then, in those ion beam analyzing apparatus, radiated ions are detected in accordance with the RBS method but a characteristic X-ray is detected in accordance with the PIXE method to make a measurement and an analysis. However, an object and a range of such analysis vary depending upon a type of an ion beam used.
In particular, in accordance with the random RBS method wherein backscattered ions from ions incident in an arbitrary direction except for to crystal axes of a specimen, a conventional ion beam having a diameter on the order of mm (hereinafter referred to simply as a large diameter beam) is used to effect a measurement of a thickness of a film and/or an evaluation of an interfacial structure of a functional thin film semiconductor or the like, a non-destructive inspection of a multi-layer structure, an evaluation of an ion implanting and diffusing process and so forth. On the other hand, a microscopic ion beam (hereinafter referred to simply as a small diameter beam) is used to effect a verification of maskless ion implanting process conditions of a functional thin film semiconductor or the like, diagnostics of a wafer after fine working, and a migration evaluation of a multi-layer wiring structure. In the meantime, in accordance with the channelling RBS method wherein backscattered ions of a large diameter parallel beam incident in parallel to a crystal axis of a specimen are measured, crystalline evaluation after etching of a crystalline thin film of an electronic material or the like, crystalline restoration of a crystalline thin film by annealing, determination of a crystal structure of a ceramic superconducting thin film, evaluation of lattice defects of a crystal surface and so forth are effected.
Further, in accordance with the PIXE method wherein a characteristic X-ray emitted from a specimen upon irradiation of ions is measured, a large diameter beam is used, and a quantitative analysis of environmental pollution elements in dust in environmental analysis, quantitative evaluation of specific trace elements in a biological structure in medical analysis or the like, identification of an age in archaeological analysis or the like and so forth are effected. Meanwhile, a small diameter beam is used when measurement of a distribution of a trace element in a cell in biological analysis or the like, chronological quantitative evaluation of environmental pollution elements contained in hair, a shell or an annual ring of a tree in environmental analysis or the like, quantitative evaluation of a trace element composition in a morbid cell in medical analysis and so forth are effected.
In this manner, an ion beam analyzing apparatus can make various measurements and analyses of a wide range depending upon the type of an ion beam used.
Therefore, investigations have been made from various aspects of system construction which can use a plurality of types of ion beams on the same apparatus, and such a multipurpose ion analyzing equipment as, for example, shown in FIG. 22 has been invented and put into practical use. The analyzing equipment is constituted such that an ion beam of a high energy emitted from an accelerator 271 is classified in ion type and energy by an ion deflecting electromagnet 272 such that ion beams are bent in three different directions and distributed to three analyzing lines 273, 274 and 275 in order that they may be used for various analyses corresponding to the characteristics thereof. Further, the ion beams distributed to the individual analyzing lines are changed into beams having predetermined forms and diameters by objective collimators and electromagnetic lenses disposed along the analyzing lines and are then introduced into specimen chambers 276, 277 and 278 disposed at terminal end portions of the individual analyzing lines 273, 274 and 275 and having individually different constructions.
In the conventional multipurpose ion analyzing equipment described above, such a construction is employed so that an analysis in accordance with the random RBS method or PIXE method which uses a small diameter beam is made on the first analyzing line 273; an analysis in accordance with the channelling RBS method which uses a parallel large diameter beam is made on the second analyzing line 274; and an analysis in accordance with the random RBS method or PIXE method which employs a large diameter beam is made on the third analyzing line 275 so that the ion analyzing equipment may cope with various analyses of a wide range with the entire system.
In an ion analyzing apparatus, if the type of an ion beam to be used can be changed variously, then it is possible to make various analyses of a wide range as described above. However, where such a conventional ion analyzing apparatus as shown in FIG. 16 is used, since the apparatus is of the type having a single function which naturally uses an ion beam of a predetermined type, that is, since the type of ions is selected by deflecting a beam emitted from an accelerator to a particular angular direction by means of a deflecting analyzing electromagnet so that an ion beam of a particular type is irradiated along a particular irradiation line upon a target, the ion analyzing apparatus can only cope with an analysis of a limited type. Therefore, such a construction is employed that, as in the conventional multipurpose ion analyzing equipment described hereinabove with reference to FIG. 22, a beam from an accelerator is selected in ion type and energy by means of an ion deflecting electromagnet such that ion beams having individually different characteristics are distributed to a plurality of analyzing lines and used for various analyses for various applications. In this instance, however, while the ion analyzing equipment can cope with various analyses of a wide range, the individual analyzing lines following the ion deflecting electromagnet must be constructed in different manners in accordance with the individual objects, and in addition to the fact that the apparatus is increased in size, the individual analyzing lines expand at individually different angles. Accordingly, there is a problem in that an increase in apparatus cost and installation spacing is invited.
Thus, the inventors have made various investigations to obtain an ion beam analyzing apparatus of a compact construction which eliminates such problems of the conventional ion beam analyzing apparatus described above and can make various analyses. As a result, a conclusion has been drawn that, in order to attain the object, it is most effective (1) to changeably select an ion beam of a particular type and permit the same to be irradiated along a same beam irradiation axial line upon a target and (2) to introduce ion beams of various types to be irradiated along the same beam irradiation axial line into a same specimen chamber so as to enable the ion beams of the various types having different characteristics to be selectively used to make various analyses.
Then, various investigations have been made to put them into practice. As a result, it has been found out that the subject (1) to changeably select an ion beam of a particular type and permit the same to be irradiated along the same beam irradiation axial line upon a target can be realized if such a construction that an objective collimator is disposed just on the downstream of an accelerator while an ion type and energy analyzing component (for example, a Wien (E.times.B) type mass spectrograph) is disposed between the objective collimator and an electromagnet lens, is employed. However, a specimen chamber of a construction which selectively introduces ion beams of various types to be irradiated along a same beam irradiation axial line and can make an analysis selectively using the ion beams of various types having different characteristics is still unknown, and a specimen chamber of a new construction which achieves the object is required.